A prospective study of the prevalence, incidence, clinical characteristics, prognostic features, and pathologic description of cystic fibrosis arthropathy (CFA). CFA is characterized by recurrent, often painful bouts of mono-or polyarthritis. Many patients also manifest an erythema-nodosum-like rash, or in a few cases, purpuric skin lesions. The flares of joint inflammation last from one day to several weeks. Some patients with CFA progress to a chronic arthritis that can be quite debilitating. The appropriate treatment of CFA is not known and has not been studied in a large prospective study. The study is being performed simultaneously at Children's Hospital and The Massachusetts General Hospital as a combined effort of the Rheumatology Departments and Cystic Fibrosis Centers at each institution. The study entails screening for the presence of CFA with a questionnaire and follow-up medical chart review, physical exam, laboratory tests and selective radiographs. The study seeks to advance both the clinical and basic scientific knowledge of CFA and possibly gain insight into possible preventive or treatment measures.